Bluetooth and wireless local area network (LAN) techniques using a 2.4 GHz industrial scientific medical (ISM) frequency band generally employ spread spectrum methods such as a frequency hopping spread spectrum (FHSS) method and a direct sequence spread spectrum (DSSS) method.
The DSSS method is adapted to obtain a spread signal by multiplying data by a spread code, and the FHSS method is adapted to shift a frequency band according to a spread code. In particular, the FHSS method transmits a signal to be spread while hopping its carrier frequencies at intervals of a predetermined time according to a hopping pattern, and converts a narrowband signal into a wideband signal over a time average. This FHSS method generates a random hopping pattern in an ISM band suitable to the standard of each country and transmits data at a frequency based on the generated pattern, resulting in the advantages of minimizing frequency overlap, reducing losses by a multipath owing to fast frequency conversion and being simple in construction. As a result, at the present, the FHSS method is widely used in low-price-type wireless devices (for example, Bluetooth devices).
However, the FHSS method has a disadvantage in that the hopping is performed irrespective of the presence or absence of an interference source over the entire frequency band, resulting in occurrence of a packet loss when the hopping is made to a specific frequency where interference is present. In this case, data (voice, audio and video) to be transmitted in real time cannot help suffering a degradation in quality if no error recovery is made.